This invention relates to relief valves. More specifically, it relates to relief valves of the type responsive to predetermined thermal and/or pressure conditions.
Prior art of possible relevance includes U.S. Pat. Nos. 3,396,449, issued Aug. 13, 1968 to Brantner; 3,471,087 issued Oct. 7, 1969 to Caparone et al; and 3,554,223 issued Jan. 12, 1971 to Shea.
Relief valves of the type providing relief in a fluid system in response to a predetermined pressure and/or thermal condition frequently employ a valve body having a valve seat which is normally closed by a poppet valve. In the usual case, the pressure setting of the valve is achieved by compressing a biasing spring for the valve to a desired degree, usually through the advancement of a nut or the like engaging one end of the spring through a bore. A significant disadvantage to this approach is economical, since the valve body typically is cast. It must be made of sufficient dimension so as to provide enough length in the bore to allow the desired adjustment. As a consequence, castings of which the valve bodies are formed are relatively large and, therefore, expensive.
Moreover, the threading of the bore is a costly manufacturing operation. In addition, typically some sort of seal must be provided to seal the interface of the threaded adjustment nut and the threaded bore, further increasing the cost. And, of course, with the large number of parts required, assembly labor expenses are commensurately increased.
In order to overcome these disadvantages, certain prior art constructions employ retainers for biasing the springs which are self-locking within a smooth bore in the body, usually by providing a sharp edge at some location on the retainer which bites into the sides of the bore. In the usual case, such sharp edges are structured so that the retainer cannot be easily removed from the bore. However, in such constructions, the retainer can be further advanced into the bore, thereby compressing the spring further and raising the pressure setting of the valve. Such movement of the retainer can occur accidentally due to jolts of the valve while in transit, or can occur through negligence on the part of the installer of the valve or the user of the valve.
In such a case, the pressure setting of the valve can be increased sufficiently so that it will not relieve thermal or pressure stresses in the system in which it is used at the desired thermal or pressure condition, possibly resulting in grave overloading of the system and rupture of parts thereof.